A/c-Heater System - Automatic Lexus ES XV10

A/C SYSTEM SPECIFICATIONS

A/C SYSTEM SPECIFICATIONS

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

Automatic A/C-Heater System Wiring Diagram (ES300). Scheme 1

DESCRIPTION

An Electronic Control Unit (ECU), located within A/C control assembly, automatically controls all A/C and heating functions. Manual controls allow the driver to select air distribution mode and desired temperature. In addition to normal A/C system components, automatic A/C-heater system includes various motors, controls and sensors. (Scheme 2) The system has self-diagnostic capabilities.

Scheme 2

SYSTEM CONTROLS

The A/C-heater control assembly consists of a liquid crystal display, a temperature control knob and various push buttons which activate A/C-heater system, set desired temperature, direct discharged air to desired outlets, activate rear defogger and control blower fan speed. (Scheme 3)

Scheme 3

HEATER WATER CONTROL VALVE

Disconnect heater water control valve cable, located in heater inlet line near firewall. Turn ignition on. Press A/C button. Set temperature control knob to maximum cool position (counter-clockwise). Set heater water control valve to cool position. Install control cable, and secure it using clamp. (Scheme 4)

Scheme 4

TROUBLE SHOOTING

Note. Before removing radio or disconnecting battery, obtain anti-theft code number from customer. After servicing, turn radio on. Word CODE will be displayed. Enter 5-digit code to restore radio operation.

Note. To measure voltage while testing or trouble shooting system, only use a Digital Volt-Ohmmeter (DVOM).

SELF-DIAGNOSTICS

A/C control assembly monitors system circuits and stores a code in memory if a problem is detected. To retrieve stored codes, see RETRIEVING CODES . Codes are displayed at temperature display.

Indicator Check

1. While pressing and holding temperature control knob and left side of fan (down) button, turn ignition on. Indicators will flash and tone will sound as a check. Press OFF button to cancel indicator check. After indicator check is complete, system will automatically enter diagnostic code check mode. Stored trouble codes will appear in sequence on the temperature display panel. See «AUTOMATIC A/C-HEATER SYSTEM TROUBLE CODES»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table.
2. Press left side of MODE button to display codes one at a time. If tone sounds when code is displayed, problem causing code currently exists. If tone does not sound when code is displayed, associated problem is past history and does not currently exist. Press OFF button to exit self-diagnostics.

AUTOMATIC A/C-HEATER SYSTEM TROUBLE CODES

CLEARING CODES

Remove ECU-B fuse from fuse block under left side of instrument panel for 10 seconds or longer. After reinstalling fuse, ensure only normal code (Code 00) appears.

ACTUATOR CHECK

1. Perform INDICATOR CHECK under «RETRIEVING CODES»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic). When system enters diagnostic code check mode, press fan (down) button. Each mode door, motor and relay will operate at one-second intervals. Press left side of MODE button to display codes one at a time and to step through checks one at a time.
2. Check airflow and temperature by hand. Tone will sound each time display code changes. Each display code is associated with a system operating condition. (Scheme 5) Press OFF button to cancel actuator check mode.

Scheme 5

CODE 11 IN-VEHICLE TEMPERATURE SENSOR CIRCUIT

1. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Turn ignition on. Using DVOM, backprobe terminals TR (Green/Yellow wire) and SG (White/Red wire) of A/C control assembly harness connector. (Scheme 6)
2. Measure circuit voltage while heating sensor. See «IN-VEHICLE TEMPERATURE SENSOR CIRCUIT VOLTAGE SPECIFICATIONS»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. IN-VEHICLE TEMPERATURE SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Sensor Temperature (1) Volts 77°F (25°C) 1.8-2.2 104°F (40°C) 1.2-1.6 (1) As temperature increases, voltage should gradually decrease.
3. If circuit voltage is not as specified, test in-vehicle sensor. See «IN-VEHICLE TEMPERATURE SENSOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__in-vehicle-temperature-sensor) under TESTING. Replace sensor if it is defective. If sensor is okay, go to next step.
4. Check wiring harness and connectors between sensor and A/C control assembly. Repair harness and connectors as necessary. If wiring harness and connectors are okay, temporarily substitute known good A/C control assembly. Retest system.

A/C Control Assembly Harness Connector Terminal ID. Scheme 6

CODE 12 OUTSIDE TEMPERATURE SENSOR CIRCUIT

1. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Turn ignition on. Using DVOM, backprobe terminals TAM (Black/Red wire) and SG (White/Red wire) of A/C control assembly harness connector. (Scheme 6)
2. Measure circuit voltage while heating outside temperature sensor. See «OUTSIDE TEMPERATURE SENSOR CIRCUIT VOLTAGE SPECIFICATIONS»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. OUTSIDE TEMPERATURE SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Sensor Temperature (1) Volts 77°F (25°C) 1.35-1.75 104°F (40°C) 0.85-1.25 (1) As temperature increases, voltage should gradually decrease.
3. If circuit voltage is not as specified, test sensor. See «OUTSIDE TEMPERATURE SENSOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__outside-temperature-sensor) under TESTING. Replace sensor if it is defective. If sensor is okay, go to next step.
4. Check wiring harness and connectors between sensor and A/C control assembly. Repair harness and connectors as necessary. If wiring harness and connectors are okay, temporarily substitute known good A/C control assembly. Retest system.

CODE 13 EVAPORATOR TEMPERATURE SENSOR CIRCUIT

1. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Turn ignition on. Using DVOM, backprobe terminals TE (Blue/White wire) and SG (White/Red wire) of A/C control assembly harness connector. (Scheme 6)
2. Measure evaporator temperature sensor circuit voltage. See «EVAPORATOR TEMPERATURE SENSOR CIRCUIT VOLTAGE SPECIFICATIONS»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. EVAPORATOR TEMPERATURE SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Sensor Temperature (1) Volts 32°F (0°C) 2.0-2.4 59°F (15°C) 1.4-1.8 (1) As temperature increases, voltage should gradually decrease.
3. If circuit voltage is not as specified, test evaporator temperature sensor. See «EVAPORATOR TEMPERATURE SENSOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__evaporator-temperature-sensor) under TESTING. Replace sensor if it is defective. If sensor is okay, go to next step.
4. Check wiring harness and connectors between sensor and A/C control assembly. Repair harness and connectors as necessary. If wiring harness and connectors are okay, temporarily substitute known good A/C control assembly. Retest system.

CODE 14 WATER TEMPERATURE SENSOR CIRCUIT

1. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Turn ignition on. Using DVOM, backprobe terminals TW (Yellow/Black wire) and SG (White/Red wire) of A/C control assembly harness connector. (Scheme 6) Measure sensor circuit voltage. See «WATER TEMPERATURE SENSOR CIRCUIT VOLTAGE SPECIFICATIONS»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. WATER TEMPERATURE SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Sensor Temperature (1) Volts 32°F (0°C) 2.8-3.2 104°F (40°C) 1.8-2.2 158°F (70°C) 0.9-1.3 (1) As temperature increases, voltage should gradually decrease.
2. If circuit voltage is not as specified, test water temperature sensor. See «WATER TEMPERATURE SENSOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__water-temperature-sensor) under TESTING. Replace sensor if it is defective. If sensor is okay, go to next step.
3. Check wiring harness and connectors between sensor and A/C control assembly. Repair harness and connectors as necessary. If wiring harness and connectors are okay, temporarily substitute known good A/C control assembly. Retest system.

CODE 21 SOLAR SENSOR CIRCUIT

Note. If testing is done in a dark area, Code 21 may occur even though system is normal. Shine a light at solar sensor and recheck for Code 21.

1. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Turn ignition on. Using DVOM, backprobe terminals S5 (Blue wire) and TS (White wire) of A/C control assembly harness connector. (Scheme 6) Measure sensor circuit voltage. See «SOLAR SENSOR CIRCUIT VOLTAGE»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) SPECIFICATIONS table. SOLAR SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Condition (1) Volts Sensor Subjected To Bright Light Less Than 4.0 Sensor Covered By Cloth 4.0-4.5 (1) As light intensity decreases, voltage should increase.
2. If circuit voltage is not as specified, test solar sensor. See «SOLAR SENSOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__solar-sensor) under TESTING. Replace sensor if it is defective. If sensor is okay, go to next step.
3. Check wiring harness and connectors between sensor and A/C control assembly. Repair harness and connectors as necessary. If wiring harness and connectors are okay, temporarily substitute known good A/C control assembly. Retest system.

CODE 22 COMPRESSOR LOCK SENSOR CIRCUIT

1. Ensure drive belt is installed properly, and belt tension is correct. Start engine. Turn blower and A/C on. Observe compressor. If compressor locks during operation, repair compressor. If compressor does not lock during operation, test compressor lock sensor. See «COMPRESSOR LOCK SENSOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__compressor-lock-sensor) under TESTING.
2. Replace compressor lock sensor if it is defective. If sensor is okay, check wiring harness and connectors between sensor and A/C control assembly. Repair harness and connectors as necessary. If wiring harness and connectors are okay, temporarily substitute known good A/C control assembly. Retest system.

CODE 23 PRESSURE SWITCH CIRCUIT

1. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Install manifold gauge set. Turn ignition on. Using DVOM, backprobe terminal PSW (Red/Blue wire) of A/C control assembly harness connector and ground. (Scheme 6)
2. Start engine. Turn A/C on. Pressure switch operation should be as shown. (Scheme 7) If pressure switch operation is not as specified, go to next step. If pressure switch operation is as specified, circuit is okay.
3. Unplug pressure switch connector, located below battery. Check for continuity between switch terminals at refrigerant pressures shown. (Scheme 8) Replace pressure switch if operation is not as specified. If switch is okay, check wiring harness and connectors between switch and A/C control assembly. If wiring harness and connectors are okay, substitute known good A/C control assembly. Retest system.

Scheme 7

Scheme 8

CODE 31 OR 41 AIR MIX DOOR POSITION SENSOR CIRCUIT

Note. For Code 41, see CODE 41 AIR MIX SERVOMOTOR CIRCUIT for additional trouble shooting procedures.

1. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Turn ignition on. Using DVOM, backprobe terminals TP (Black/Yellow wire) and SG (White/Red wire) of A/C control assembly harness connector. (Scheme 6)
2. Measure sensor circuit voltage while changing set temperature to activate air mix door. See «AIR MIX DOOR POSITION SENSOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) CIRCUIT VOLTAGE table. AIR MIX DOOR POSITION SENSOR CIRCUIT VOLTAGE Set Temperature (1) Volts Maximum Cool 3.5-4.5 Maximum Hot 0.5-1.8 (1) As set temperature increases, voltage should gradually decrease.
3. If circuit voltage is not as specified, test air mix servomotor. See «AIR MIX SERVOMOTOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under TESTING. Replace servomotor if it is defective. If servomotor is okay, go to next step.
4. Check wiring harness and connectors between sensor and A/C control assembly. Repair harness and connectors as necessary. If wiring harness and connectors are okay, temporarily substitute known good A/C control assembly. Retest system.

CODE 32 OR 42 AIR INLET DOOR POSITION SENSOR CIRCUIT

Note. For Code 42, see CODE 42 AIR INLET SERVOMOTOR CIRCUIT for additional trouble shooting procedures.

1. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Turn ignition on. Using DVOM, backprobe terminals TPI (Blue/Yellow wire) and SG (White/Red wire) of A/C control assembly harness connector. (Scheme 6)
2. Measure sensor circuit voltage while alternately pressing fresh air and recirculated air buttons to activate air inlet door. See «AIR INLET DOOR POSITION CIRCUIT VOLTAGE SPECIFICATIONS»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. AIR INLET DOOR POSITION CIRCUIT VOLTAGE SPECIFICATIONS Switch Pressed (1) Volts Recirculated 3.5-4.5 Fresh 0.5-1.8 (1) As door moves from recirculated air position toward fresh air position, voltage should gradually decrease.
3. If circuit voltage is not as specified, test air inlet servomotor. See «AIR INLET SERVOMOTOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under TESTING. Replace servomotor if it is defective. If servomotor is okay, go to next step.
4. Check wiring harness and connectors between sensor and A/C control assembly. Repair harness and connectors as necessary. If wiring harness and connectors are okay, temporarily substitute known good A/C control assembly. Retest system.

CODE 41 AIR MIX SERVOMOTOR CIRCUIT

Note. See CODE 31 OR 41 AIR MIX DOOR POSITION SENSOR CIRCUIT for additional trouble shooting procedures.

1. Warm engine to normal operating temperature. Perform RETRIEVING CODES. After system enters diagnostic code check mode, perform ACTUATOR CHECK.
2. Press left side of MODE button to enter step mode and display codes. See «AIR MIX DOOR AIRFLOW»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. Air mix door operation should be as specified.
3. If air mix door functions as specified, circuit is okay. If air mix door does not function as specified, see AIR MIX SERVOMOTOR FUNCTIONAL CHECK.

AIR MIX DOOR AIRFLOW

Air Mix Servomotor Functional Check

1. Remove air mix servomotor. See «AIR MIX SERVOMOTOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Unplug air mix servomotor connector.
2. Apply battery voltage to servomotor connector terminal No. 2. (Scheme 9) Connect terminal No. 6 to ground. Air mix servomotor lever should move to cool position. Reverse battery and ground leads. Servomotor lever should move to hot position.
3. If air mix servomotor does not function as described, replace air mix servomotor. If servomotor functions correctly, check wiring harness and connectors between servomotor and A/C control assembly. Repair or replace harness and connectors as necessary. If wiring harness and connectors are okay, substitute known good A/C control assembly. Retest system.

Scheme 9

CODE 42 AIR INLET SERVOMOTOR CIRCUIT

Note. See CODE 32 OR 42 AIR INLET DOOR POSITION SENSOR CIRCUIT for additional trouble shooting procedures.

1. Warm engine to normal operating temperature. Perform «RETRIEVING CODES»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) . After system enters diagnostic code check mode, perform «ACTUATOR CHECK»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__actuator-check) .
2. Press left side of MODE button to enter step mode and display codes. See «AIR INLET DOOR AIRFLOW»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. Air inlet door operation should be as specified. AIR INLET DOOR AIRFLOW Code Door Position 20-22 Fresh Air 23 Fresh/Recirculated Air 24-29 Recirculated Air
3. If air inlet door functions as specified, circuit is okay. If air inlet door does not function as specified, test air inlet servomotor. See «AIR INLET SERVOMOTOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under TESTING.

Air Inlet Servomotor Functional Check

1. Remove air inlet servomotor. See «AIR INLET SERVOMOTOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Unplug air inlet servomotor connector.
2. Connect battery voltage to air inlet servomotor connector terminal No. 2. (Scheme 10) Connect terminal No. 1 to ground. Air inlet servomotor lever should move to recirculated air position. Reverse battery and ground connections. Air inlet servomotor lever should move to fresh air position.
3. If air inlet servomotor does not operate as specified, replace air inlet servomotor assembly. If servomotor operates correctly, check wiring harness and connectors between servomotor and A/C control assembly. Repair or replace harness and connectors as necessary. If wiring harness and connectors are okay, substitute known good A/C control assembly. Retest system.

Scheme 10

TESTING

Note. Before removing radio or disconnecting battery, obtain anti-theft code number from customer. After servicing, turn radio on. Word CODE will be displayed. Enter 5-digit code to restore radio operation.

ACCESSORY POWER CIRCUIT

1. Turn ignition on. Check CIG/RADIO fuse at fuse block under left side of instrument panel. If fuse is okay, go next step. If fuse is blown, correct cause and replace fuse.
2. Turn ignition off. Remove console upper panel. Remove A/C control assembly, leaving harness connectors attached. Turn ignition on. Using DVOM, backprobe between A/C control assembly 8-pin connector terminal ACC (Blue/Red wire) and body ground. (Scheme 6) If battery voltage does not exist, repair Blue/Red wire between connector and CIG/RADIO fuse.

Scheme 11

1. Unplug air inlet servomotor connector. See «AIR INLET»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) SERVOMOTOR under REMOVAL & INSTALLATION. Measure resistance between servomotor connector terminals No. 4 and 5. (Scheme 11)
2. Resistance should be 4700-7200 ohms. If resistance is not as specified, replace air inlet servomotor. If resistance is as specified, go to next step.
3. Connect ohmmeter between terminals No. 3 and 5. Connect battery voltage to terminal No. 2. (Scheme 10) Connect terminal No. 1 to ground. Reverse power leads. Resistance should be as specified for each door position. See «AIR INLET DOOR POSITION RESISTANCE»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) SPECIFICATIONS table.

AIR INLET DOOR POSITION RESISTANCE SPECIFICATIONS

Scheme 12

1. Remove air mix servomotor. See «AIR MIX SERVOMOTOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Unplug air mix servomotor connector. Measure resistance between servomotor connector terminals No. 1 and 3. (Scheme 12)
2. Resistance should be 4700-7200 ohms. If resistance is not as specified, replace air mix servomotor. See «AIR MIX SERVOMOTOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. If resistance is as specified, go to next step.
3. Connect ohmmeter between servomotor terminals No. 1 and 4. Apply battery voltage to air mix servomotor connector terminal No. 2. (Scheme 9) Connect terminal No. 6 to ground. Measure resistance between terminals No. 1 and 4. Reverse power leads. Resistance should be as specified for each door position. See «AIR MIX DOOR POSITION»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) RESISTANCE SPECIFICATIONS table.

AIR MIX DOOR POSITION RESISTANCE SPECIFICATIONS

1. Warm engine to normal operating temperature. Perform «RETRIEVING CODES»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) . After system enters diagnostic code check mode, perform «ACTUATOR CHECK»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__actuator-check) .
2. Press left side of MODE button to enter step mode and display codes. See «AIR OUTLET DOOR AIRFLOW»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. Air outlet door operation should be as specified. AIR OUTLET DOOR AIRFLOW Code Airflow Mode 20-24 Face 25 Bi-Level 26-27 Foot 28 Foot-Defrost 29 Defrost
3. If air outlet door servomotor functions as specified, circuit is okay. If air outlet door does not function as specified, check air outlet servomotor. See AIR OUTLET SERVOMOTOR FUNCTIONAL CHECK.

Air Outlet Servomotor Functional Check

1. Remove air outlet servomotor. See «AIR OUTLET SERVOMOTOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Unplug air outlet servomotor connector.
2. Apply battery voltage to air outlet servomotor connector terminal No. 6. (Scheme 13) Connect terminal No. 7 to ground. Air outlet servomotor lever should move to specified position when appropriate terminal is grounded. See «AIR OUTLET SERVOMOTOR LEVER»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) POSITIONS table.
3. Replace air outlet servomotor if it does not operate as specified. If servomotor operates correctly, check wiring harness and connectors between servomotor and A/C control assembly. If wiring harness and connectors are okay, substitute known good A/C control assembly. Retest system.

Scheme 13

AIR OUTLET SERVOMOTOR LEVER POSITIONS

BACK-UP POWER CIRCUIT

1. Turn ignition off. Check ECU-B fuse at fuse block under left side of instrument panel. If fuse is okay, go next step. If fuse is blown, correct cause and replace fuse.
2. Remove A/C control assembly, leaving harness connectors attached. Turn ignition on. Using DVOM, backprobe between A/C control assembly 8-pin connector terminal +B (Blue/Yellow wire) and body ground. (Scheme 6) If battery voltage does not exist, repair Blue/Yellow wire between connector and ECU-B fuse.

BLOWER MOTOR CIRCUIT

1. Turn ignition off. Remove blower motor. See «BLOWER MOTOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Connect battery voltage to terminal No. 2 of blower motor. Connect terminal No. 1 to ground. If blower motor runs smoothly, go to next step. Replace blower motor if it does not run smoothly.
2. Check wiring between blower motor and battery and between blower motor and ground. Repair the wiring as necessary. See «WIRING DIAGRAM»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) .

Scheme 14

1. Turn ignition on. Check GAUGE fuse at fuse block under left side of instrument panel. If fuse is okay, go next step. If fuse is blown, correct cause and replace fuse.
2. Turn ignition off. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Start engine. Using DVOM, backprobe A/C control assembly connector terminal MGC (Blue/Yellow wire) and body ground. (Scheme 6) Press A/C button. Voltmeter should indicate less than one volt. Press OFF button. Voltmeter should indicate battery voltage. If operation is as specified, go to next step. If operation is as not as specified, go to step 7).
3. Remove compressor clutch relay from relay box No. 5, located at left side of engine compartment, toward rear. Measure resistance between terminals No. 1 and 2. (Scheme 14) Resistance should be 62.5-90.9 ohms. Check for continuity between terminals No. 3 and 5. Continuity should not exist.
4. Connect battery voltage to terminal No. 1 of relay. Connect terminal No. 2 to ground. Check for continuity between terminals No. 3 and 5. Continuity should exist. If relay operates as specified, go to next step. Replace relay if it does not operate as specified.
5. Unplug connector from compressor clutch. Apply battery voltage to compressor clutch connector terminal No. 4 (Black/White wire). If clutch engages, go to next step. If clutch does not engage, repair or replace compressor clutch.
6. Check wiring and connectors associated with compressor relay and compressor. Repair or replace wiring and connectors as necessary. If wiring and connectors are okay, go to next step.
7. Turn ignition off. Unplug 23-pin connector from A/C control assembly. Turn ignition on. Check for voltage at harness connector terminal AC1. If battery voltage exists, go to next step. If battery voltage does not exist, substitute a known good engine/electronically controlled transmission ECU. Retest system.
8. Connect wiring to A/C control assembly. Backprobe terminal AC1 (Black/Yellow wire) of 23-pin connector and ground. (Scheme 6) Start engine. Press AUTO button. Cycle A/C system on and off by pressing A/C button. With compressor clutch engaged, meter should indicate less than one volt. With compressor clutch disengaged, meter should indicate battery voltage. If readings are as specified, go to next step. If readings are not as specified, substitute a known good A/C control assembly. Retest system.
9. Start engine. Press AUTO button. Cycle A/C system on and off by pressing A/C button. With A/C system off, meter should indicate less than 1.5 volts. With A/C system on, meter should indicate battery voltage. If readings are not as specified, go to next step. If readings are as specified, substitute a known good A/C control assembly. Retest system.
10. Check wiring and connectors associated with A/C control assembly and engine/electronically controlled transmission ECU. Repair or replace wiring and connectors as necessary. If wiring harnesses and connectors are okay, go to next step.
11. Turn ignition off. Remove glove box. Unplug connectors from engine/electronically controlled transmission (ECU). Turn ignition on. Press A/C button to turn system on. Measure voltage between terminal ACT (Light Green/Red wire) on engine/electronically controlled transmission ECU and ground. (Scheme 15) If battery voltage exists, substitute a known good ECU. Retest system.

Scheme 15

COMPRESSOR LOCK SENSOR

Unplug compressor lock sensor connector, located at compressor. Measure resistance between terminals No. 1 and 2 of sensor at temperatures specified. (Scheme 16) See COMPRESSOR LOCK SENSOR RESISTANCE SPECIFICATIONS table. Replace sensor if resistance is not as specified.

Scheme 16

COMPRESSOR LOCK SENSOR RESISTANCE SPECIFICATIONS

EVAPORATOR TEMPERATURE SENSOR

Remove evaporator temperature sensor, located at evaporator. Measure the sensor resistance at temperatures specified. See EVAPORATOR TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS table. If resistance is not as specified, replace sensor.

EVAPORATOR TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS

1. Perform «RETRIEVING CODES»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic). After system enters diagnostic code check mode, perform «ACTUATOR CHECK»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__actuator-check). Press left side of MODE button to enter step mode and display codes. See «BLOWER SPEED»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. If blower speed does not change as specified, go to next step. If blower motor speed is as specified, circuit is okay. BLOWER SPEED Code Blower Speed 21 Low 22-28 Medium 29 High
2. Remove extra-high relay, located on evaporator assembly. Measure resistance between relay terminals No. 1 and 2. (Scheme 17) Resistance should be 55.8-88.9 ohms. Check for continuity between terminals No. 3 and 4. Continuity should not exist.
3. Connect battery voltage to terminal No. 1. Connect terminal No. 2 to ground. Check for continuity between terminals. No. 3 and 4. Continuity should exist. If relay operates as specified, go to next step. Replace relay if it does not operate as specified.
4. Check wiring harness and connectors between A/C control assembly and extra-high relay and between extra-high relay and battery. Repair the harness and connectors as necessary. See «WIRING DIAGRAM»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic). If wiring harnesses and connectors are okay, substitute a known good A/C control assembly. Retest system.

Scheme 17

HEATER MAIN RELAY CIRCUIT

1. Turn ignition on. Check GAUGE fuse at fuse block under left side of instrument panel. If fuse is okay, go next step. If fuse is blown, correct cause and replace fuse.
2. Remove A/C control assembly, leaving harness connectors attached. Turn ignition off. Check for voltage between A/C control assembly 23-pin connector terminal HR (Blue/White wire) and body ground. (Scheme 6) If battery voltage does not exist, go to next step. If battery voltage exists, repair short to voltage in Blue/White wire between connector and heater main relay.
3. Turn ignition on. Check for voltage between A/C control assembly 23-pin connector terminal HR (Blue/White wire) and body ground. If battery voltage does not exist, go to next step. If battery voltage exists, circuit is okay.
4. Remove heater main relay, located behind glove box on right side. Check for continuity between terminals No. 1 and 4. (Scheme 18) Continuity should not exist. Check for continuity between terminals No. 2 and 4. Continuity should exist. Measure resistance between terminals No. 3 and 5. Resistance should be 62.5-90.9 ohms.
5. Apply battery voltage to terminal No. 3, and connect terminal No. 5 to ground. Check for continuity between terminals No. 1 and 2. Continuity should not exist. Check for continuity between terminals No. 2 and 4. Continuity should exist. Replace relay if it does not operate as specified. If relay is okay, repair wiring between 8-pin connector and battery. See «WIRING DIAGRAM»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic).

Scheme 18

IGNITION POWER & GROUND CIRCUITS

1. Turn ignition on. Check GAUGE fuse at fuse block under left side of instrument panel. If fuse is okay, go next step. If fuse is blown, correct cause and replace fuse.
2. Remove console upper panel. Remove A/C control assembly, leaving harness connectors attached. Turn ignition on. Using DVOM, backprobe 8-pin connector terminals IG+ (Red/Blue wire) and GND (White/Black wire). (Scheme 6) If battery voltage does not exist, go to next step. If battery voltage exists, circuit is okay.
3. Turn ignition off. Unplug 8-pin connector from A/C control assembly. Check Red/Blue wire between connector IG+ terminal and GAUGE fuse for continuity or short to ground. Repair wire as necessary. If wire is okay, go to next step.
4. Measure resistance between GND terminal of connector (White/Black wire) and ground. If resistance is less than one ohm, wire is okay. Repair open White/Black wire to ground if resistance is not less than one ohm.

IN-VEHICLE TEMPERATURE SENSOR

Remove in-vehicle temperature sensor. (Scheme 2) Measure sensor resistance while heating sensor. See IN-VEHICLE TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS table. If resistance is not as specified, replace sensor.

IN-VEHICLE TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS

OUTSIDE TEMPERATURE SENSOR

1. Unplug outside temperature sensor, located behind grille. Measure the sensor resistance while heating sensor. See «OUTSIDE TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table.
2. If resistance is not as specified, replace sensor. If resistance is within specification, check wiring harness and connectors between sensor and A/C control assembly. Repair harness and connectors as necessary. If wiring harness and connectors are okay, substitute a known good A/C control assembly. Retest system.

OUTSIDE TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS

POWER TRANSISTOR CIRCUIT

1. Remove power transistor. See «POWER TRANSISTOR»(/lexus/es/xv10-1991-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Unplug power transistor connector. Connect battery voltage to power transistor terminal No. 4. Connect battery voltage, through a 120-ohm resistor, to terminal No. 3 (Scheme 19).
2. Connect test light between terminal No. 2 and negative battery terminal. If test light glows, go to next step. If test light does not glow, replace power transistor. Disconnect battery leads.
3. Measure resistance between terminals No. 1 and 4. If resistance is 2000-2400 ohms, power transistor is okay. Replace power transistor if resistance is not as specified.

Scheme 19

SELF-DIAGNOSTIC CIRCUIT

Turn ignition on. Measure voltage between terminals TC and E1 of diagnostic connector, located under left side of instrument panel. (Scheme 20) If meter indicates battery voltage, circuit is okay. If meter does not indicate battery voltage, check wiring and connectors associated with A/C control assembly and diagnostic connector. If wiring is okay, substitute a known good A/C control assembly. Retest system.

Scheme 20

SOLAR SENSOR

Remove solar sensor from top of instrument panel. Unplug harness connector. Cover sensor using cloth. Measure resistance between sensor terminals. Remove cloth. Subject sensor to bright light and measure resistance between terminals of sensor. See SOLAR SENSOR RESISTANCE SPECIFICATIONS table. If resistance is not as specified, replace sensor.

SOLAR SENSOR RESISTANCE SPECIFICATIONS

WATER TEMPERATURE SENSOR

Remove coolant temperature sensor, located at heater core. Place sensor and thermometer in water. Measure resistance between sensor terminals as water is heated. If resistance is not as specified, replace water temperature sensor. See WATER TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS table.

WATER TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS

REMOVAL & INSTALLATION

Note. Before removing radio or disconnecting battery, obtain anti-theft code number from customer. After servicing, turn radio on. Word CODE will be displayed. Enter 5-digit code to restore radio operation.

Disconnect negative battery cable. Remove 4 bolts retaining radio and A/C control assembly to instrument panel. Remove 8 bolts, 4 screws and brackets. Separate radio from A/C control assembly. To install, reverse removal procedure.

Disconnect negative battery cable. Remove glove box. Remove ECU and bracket. Unplug servomotor connector. Remove servomotor. To install servomotor, reverse removal procedure.

Disconnect negative battery cable. Remove dashboard lower finish panel, safety pad and air duct. Unplug servomotor connector. Remove servomotor. Disconnect control cable. To install, reverse removal procedure.

Disconnect negative battery cable. Remove dashboard lower finish panel, safety pad and air duct. Unplug servomotor connector. Remove servomotor. To install, reverse removal procedure.

Disconnect negative battery cable. Remove lower dashboard panel and undercover. Remove connector bracket. Remove blower motor. To install, reverse removal procedure.

1. If compressor runs, idle engine for 10 minutes with A/C on. Turn ignition off. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove battery and tray. Remove radiator fan. Unplug compressor connector.
2. Disconnect and cap refrigerant hoses from compressor. Loosen drive belt. Remove compressor bolts and compressor. If replacing compressor, add 3.5 ounces refrigerant oil to compressor. To install, reverse removal procedure. Evacuate and recharge system. Check system for leaks.

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove battery, upper cover and radiator fan. Disconnect and plug refrigerant lines at condenser.
2. Remove headlights. Pull condenser upward from between radiator and body. If replacing condenser, add 1.2 ounces refrigerant oil to condenser. To install, reverse removal procedure. Evacuate and recharge system. Check system for leaks.

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Disconnect and plug refrigerant lines from evaporator assembly. Remove evaporator cover and evaporator.
2. Remove evaporator assembly. If replacing evaporator, add 1.6 ounces of refrigerant oil to evaporator. To install, reverse removal procedure. Evacuate and recharge system. Check system for leaks.

1. Disconnect negative battery cable. Drain cooling system. Remove heater shield. Remove 3 retaining screws and clamps. Disconnect heater hoses. Remove heater core.
2. To install, reverse removal procedure. Refill cooling system. Start engine, and warm it to operating temperature. Check system for leaks.

Disconnect negative battery cable. Remove dashboard lower finish panel, safety pad and air duct. Unplug power transistor connector. Remove power transistor. To install, reverse removal procedure.

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Disconnect and plug liquid lines from receiver-drier.
2. Remove receiver-drier from bracket. If replacing receiver-drier, add 0.5 ounce of refrigerant oil to receiver-drier. To install, reverse removal procedure. Evacuate and recharge system. Check system for leaks.

See also:
• RETRIEVING CODES
• IN-VEHICLE TEMPERATURE SENSOR
• OUTSIDE TEMPERATURE SENSOR
• EVAPORATOR TEMPERATURE SENSOR
• WATER TEMPERATURE SENSOR
• SOLAR SENSOR
• COMPRESSOR LOCK SENSOR
• CODE 41 AIR MIX SERVOMOTOR CIRCUIT
• CODE 42 AIR INLET SERVOMOTOR CIRCUIT
• CODE 31 OR 41 AIR MIX DOOR POSITION SENSOR CIRCUIT
• CODE 32 OR 42 AIR INLET DOOR POSITION SENSOR CIRCUIT
• ACTUATOR CHECK